Spark plug gap

I have a 1999 pontiac grand prix gtp, it has 1.9 roller rockers undersize 3.1 pulley ported and polished heads, ported and polished blower 3.5 inch downpipe with cat delete and the computer has a tune on it as well from ZZ performance on 93 octane with kr, I'm looking to replace my spark plugs but am not sure how to determine my spark gap with the modifications that have been done, the car makes around 340hp and boost peaks at 14 pounds.

1 Answer

You're going to have to go 'old school' on this. You should be running plugs 1 to 2 ranges cooler than stock as a starting point. Make sure your fuel ratio isn't too rich or lean. Set the gap slightly tighter than stock, but no smaller than .032. Again, this is your starting point. Run the car for 300 miles, pay attention to the way it's running of course and make any timing/fuel adjustments you need to get the best performance. Pull the plugs, and inspect them for heat damage (plug range is too hot) or fouling (too cold). If the plugs look correct, you can begin to zero in on the right gap. Try opening the gap until you get misfires at 3500rpm+. You want the gap to be as wide as it can be without affecting performance. Good luck!

On two separate occasions my car started missing because the electrode was sitting
on the firing pin. The second time it happened after a hard acceleration. It has 183000
on it. Previous owner insta...

Content submitted by Users is not endorsed by CarGurus, does not express the opinions of CarGurus, and should not be considered reviewed, screened, or approved by CarGurus. Please refer to CarGurus Terms of Use.